I actually think Tatiana tends to dress very modest if modesty is about not showing one's body.
We're all a bit excited about the baby arrival, aren't we? We were thinking the baby would be born in January because some magazines told us about it right? Was it Tatiana who said it? In a link posted a few posts ago, it says it will be born in March. I guess that's the right date.
The first confirmation we had about Tatiana being pregnant was when she received that award in Madrid. Remember the pics here:
http://realeza.blogs.sapo.pt/689999.html
It was early November. Her belly was perfectly visible in the first set of pics, with a "tight" dress but in the second set of pics anyone could have doubts about whether she was pregnant or not. If she was to give birth in January she was 6 (if late january) or 7(if early january) in november. I don't think that was the case. If she's to give birth in March she was 5(if early march) or 4(if late march).
EDIT: The first time we were induced to think Tatiana was pregnant was in mid July when they were photographed in Monaco
http://realeza.blogs.sapo.pt/597265.html
Tatiana seems to have a belly there and since they had just announced their engagement, everyone thought she was pregnant, I think.
It's likely that she was pregnant then, but only one or two months, not enought to be showing a bump just yet, right?
Remember that Tatiana was never a slim woman, she always had some weight and even a bit belly as well as her weight seems to flutuate a bit, tought it doesn't show so much because she "hides" it in her hippie clothes. Also, some woman have naturally a more prominent belly than others and could easily be mistaken by early pregnancies sometimes (I know, that happens to me, unfortunately). Tatiana seems to be the case.
So the pregnancy doesn't seem to last forever, it's just that when we first saw a bump, there was no pregnancy bump yet, so we were mislead.